[Sync] Replacing NULL with nullptr/null throughout sync code.

chrome/browser/sync/test/integration/sync_datatype_helper.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/sync/test/integration/sync_datatype_helper.h"
 
 #include "chrome/browser/sync/test/integration/sync_test.h"
 
 namespace {
 
 // The SyncTest instance associated with sync_datatype_helper.
-static SyncTest* test = NULL;
+static SyncTest* test = nullptr;
 
 }  // namespace
 
 namespace sync_datatype_helper {
 
 void AssociateWithTest(SyncTest* test) {
-  ASSERT_TRUE(test != NULL) << "Cannot associate with null test.";
-  ASSERT_TRUE(::test == NULL) << "Already associated with a test.";
+  ASSERT_TRUE(test != nullptr) << "Cannot associate with null test.";
+  ASSERT_TRUE(::test == nullptr) << "Already associated with a test.";
   ::test = test;
 }
 
 SyncTest* test() {
-  EXPECT_TRUE(::test != NULL) << "Must call AssociateWithTest first.";
+  EXPECT_TRUE(::test != nullptr) << "Must call AssociateWithTest first.";
   return ::test;
 }
 
 }  // namespace sync_datatype_helper